Some earth-boring tools are configured to selectively actuate to enable the earth-boring tools to engage with an earth formation. For example, an expandable reamer may be attached to a drill string, tripped down a borehole, and actuated within the borehole to extend blades of the expandable reamer and engage with a sidewall defining the borehole. As another example, a coring bit may be attached to a drill string, tripped down a borehole, have fluid pumped through a central bore of the coring bit at a high flow rate to remove any detritus collected at the bottom of the borehole, and be actuated to redirect flow from the central bore to peripheral nozzles and clear the central bore for receipt of a core sample.
In some applications, actuation may be accomplished by dropping an actuation member (e.g., a ball) at an upper end of the drill string into a central bore of the drill string to travel down the drill string (e.g., in response to drilling fluid flowing down the central bore or under the influence of gravity) and actuate the earth-boring tool by engaging with an actuating receptacle (e.g., a ball seat or collet). In other applications, dropping the actuation member at the upper end of the drill string may not be feasible because of components in the drill string between the upper end and the actuating receptacle that may interfere with (e.g., prevent) the actuation member's travel down the drill string. For example, measuring-while-drilling instrumentation frequently relies on pulse telemetry to communicate information measured in the borehole back to the surface, which may involve placing a valve in the flow path down the central bore. The valve may open and shut frequently to create the pulses that convey information to a receiver at the surface, which valve may render passing any actuation member through the measuring-while-drilling apparatus in the drill string unfeasible. As another example, downhole motors may be used to rotate earth-boring tools, instead of using a motor at the surface to rotate the entire drill string. Rotors within downhole motors may be driven by fluid pumped down the central bore of the drill string and may block or even destroy any actuation members attempting to pass through the downhole motors.
To enable actuation of selectively actuating earth-boring tools having such interfering components located above them in the drill string, downhole actuation mechanisms have been proposed. For example, U.S. Pat. No. 6,959,766, issued Nov. 1, 2005, to Connell, the disclosure of which is incorporated herein in its entirety by this reference, discloses a downhole ball drop tool actuated by dropping a small, releasing ball down the drill string, which small, releasing ball may have a small outer diameter and pass through tools or mechanisms that have restrictive flow paths. The releasing ball engages with a seat, building pressure of the drilling fluid until the seat and its associated sleeve move down and rotate rocker arms that are positioned to rotate and release an actuating ball. As another example, U.S. Pat. No. 7,624,810, issued Dec. 1, 2009, to Fould et al., the disclosure of which is incorporated herein in its entirety by this reference, discloses a ball dropping assembly for use in a well. A piston in a pocket of a ball dropping sub shears a shear pin when fluid flowing down the drill string exerts sufficient force and extends into the flow path to deploy the ball.